Occurrences of antimicrobial resistant bacteria and antimicrobial resistance genes in retail ground beef with and without a “Raised without Antibiotics” claim

Authors: Schmidt, John; Vikram, Amit; THOMAS, KEVIN - Colorado State University; Arthur, Terrance; WEINROTH, MAGGIE - Colorado State University; PARKER, JENNIFER - Colorado State University; HANES, AYANNA - Colorado State University; GEORNARAS, IFIGENIA - Colorado State University; MORLEY, PAUL - Colorado State University; Wheeler, Tommy; BELK, KEITH - Colorado State University

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 1/12/2019
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Category: Post-harvest Checkoff Funded: Yes Published: Unpublished to date. Objective: Determine levels of antibiotic resistant bacteria and antimicrobial resistance genes in retail ground beef with and without a “Raised without Antibiotics” claim. Experimental Design & Analysis: Retail ground beef samples were obtained from 6 U.S. cities. A total of 599 samples were obtained. Samples with a “Raised without Antibiotics” or USDA Organic claim (N = 299) were assigned to the “Raised without Antibiotics” production system (abbreviated “RWA”). Samples lacking a “Raised without Antibiotics” claim (N = 300) were assigned to the Conventional production system (abbreviated “CONV”) group. Each sample was cultured for the detection of the following antimicrobial resistant bacteria (ARB): tetracycline-resistant (TETr) E. coli, 3rd generation cephalosporin-resistant (3GCr) E. coli, erythromycin-resistant (ERYr) Enterococcus, vancomycin-resistant (VANr) Enterococcus, and methicillin-resistant S. aureus (MRSA). Salmonella were cultured from each sample and isolates were tested for susceptibility to 14 antimicrobials. Metagenomic DNA was isolated from each sample and qPCR was used to determine the abundance of the following antimicrobial resistance genes (ARGs): aac(6’)-Ie-aph(2”)-Ia, aadA1, blaCMY-2, blaCTX-M, blaKPC-2, mecA, erm(B), tet(A), tet(B), and tet(M). The impacts of production system and city on ARB detection were assessed by the Likelihood-ratio chi-squared test. The impact of production system on ARG abundance was assessed by two-way ANOVA. P-values < 0.05 were considered significant. Key Results: TETr E. coli and ERYr Enterococcus were detected more frequently in CONV ground beef (Figure 1). 3GCr E. coli, VANr Enterococcus, and MRSA detection did not differ by production system (Figure 1). Salmonella were detected in 7 samples; serotyping and antimicrobial resistance phenotyping results are pending. The blaCTX-M ARG was more abundant in CONV, but the aac(6’)-Ie-aph(2”)-Ia and tet(M) ARGs were more abundant in RWA (Figure 2). The abundances for the remaining 7 ARG did not differ by production system (Figure 2). How can this information be applied in the industry? Only 5 of 15 measurements of antimicrobial resistance (AMR) were statistically different between production systems. Three AMR measurements were higher in CONV, while 2 AMR measurements were higher in RWA. Thus, we conclude CONV and RWA ground beef available at retail in the U.S. harbor similar levels of AMR. These results are in general agreement with a recently published study authored by our group that examined antimicrobial resistance in CONV and RWA ground beef obtained from U.S. foodservice suppliers (Vikram et al., J. Food Prot. 81:2007-2018. 2018.). Together these studies suggest that antimicrobial use during U.S. cattle production has minimal to no impact on human exposure to AMR via ground beef in the U.S.